Magnetic coating compositions

ABSTRACT

MAGNETIC COATING COMPOSITIONS COMPRISING MAGNETIC OXIDE PIGMENT AND A BINDER SELECTED FROM CERTAIN WATERBASED ACRYLIC RESIN EMULSIONS. THE COMPOSITIONS OF THIS INVENTION ARE PARTICULARLY SUITABLE FOR IMPARTING MAGNETIC DATA FIELDS TO PAPER, CARD STOCK, FILM, OR OTHER SUBSTRATES. THEY ARE PARTICULARLY SUITABLE FOR APPLICATION TO MAGNETIC TAPES TO BE SUBJECTED TO HIGH TRANSPORT SPEEDS PAST MAGNETIC TAPE HEADS WITH WHICH INTIMATE CONTACT MUST BE MAINTAINED.

United States Patent 01 iice 3,725,285 Patented Apr. 3, 1973 3,725,285 MAGNETIC COATING COMPOSITIONS Hans H. Denk, Vienna, Va., and Joseph J. Sabad, Trenton,

N.J., assignors to International Business Machines Corporation, Armonk, N.Y. No Drawing. Filed June 24, 1970, Ser. No. 49,508 Int. Cl. Htllf 1/28 US. Cl. 252-6254 4 Claims ABSTRACT OF THE DISCLOSURE Magnetic coating compositions comprising magnetic oxide pigment and a binder selected from certain Waterbased acrylic resin emulsions. The compositions of this invention are particularly suitable for imparting magnetic data fields to paper, card stock, film, or other substrates. They are particularly suitable for application to magnetic tapes to be subjected to high transport speeds past magnetic tape heads with which intimate contact must be maintained.

BACKGROUND OF THE INVENTION [Field of the invention The present invention relates to magnetic coating compositions to be employed for imparting magnetic data fields to various substrates.

Description of the prior art Magnetic coating compositions containing magnetic oxide particles suspended in a binder composition including a volatile organic solvent are Well known. Although such compositions can be advantageously employed to produce suitable magnetic recording elements, the use of such compositions often results in various disadvantages, including the necessity to employ lengthy mixing and milling operations as well as the need to employ extended curing periods under elevated temperatures. In addition to the extended periods of time required for the preparation of magnetic recording elements employing a solvent base magnetic coating composition, some loss of the binder material may be incurred due to the fact that the binder, being in solution, can be carried into the substrate, thus depriving the magnetic pigment of its full complement of binder. In addition, in such systems, some of the oxide may accompany the binder into more porous substrates, causing signal-to-signal ratios which are excessive. Further, the nature of the substrate may be limited in accordance with the solvent employed in the coating composition. Additional disadvantages arise from the fact that many organic solvents are highly flammable and/or toxic to operating personnel, giving rise to the necessity of providing suitable explosion-proof hanthing and exhaust systems.

As a result of these disadvantages, it has been previously proposed in the art to employ dispersions of mag netic pigments in aqueous resin systems. it has been considered that the use of such compositions would eliminate many of the disadvantages discussed above relating to the presence of a volatile organic solvent. For example, the use of aqueous resin emulsions in such compositions would allow the direct use of resins prepared via emulsion polymerization with the cost saving attendant thereto. Further, in such systems, the water present in the coating composition acts only as a carrier. That is, the discrete resin particles, together with the magnetic pigment, remain at the surface of the substrate until the water is dissipated, thus eliminating the problem of the possible loss of binder and/or magnetic oxide into the substrate. The absence of a volatile organic solvent, of course, decreases cost and eliminates the need for special systems to avoid the possibility of explosions and toxicity hazards.

An example of a proposal to use Water-based magnetic coating compositions is the disclosure of Colwill et al. in US. Pat. No. 3,023,123 and by lLevine in US. application Ser. No. 777,558, now abandoned, but referred to in the foregoing patent. These disclosures are directed to magnetic coating compositions comprising an aqueous vehicle containing a dispersing agent, at least 7.5% by weight of discrete resin particles in the form of a synthetic latex dispersion, at least 20% by weight of ferromagnetic iron oxide particles in suspension and at least 0.4% by weight of a water soluble algin. The Colwill et al. and Levine disclosures are primarily directed to the use of an aqueous styrene-butadiene copolymer latex. However, there is also disclosed the use of acrylic latex dispersions such as Rhoplex B-lS and Rhoplex B--A. In practice, however, several difficulties have been encountered with such compositions. Among them are a tendency toward blocking at elevated temperatures and deformation of the coating under conditions of high transport speeds past write/ read heads with which intimate contact must be maintained. Additional problems which have been encountered with such coatings relate to handling and include poor adhesion, poor abrasion resistance, and poor wet rub strength.

SUMMARY OF THE INVENTION Applicants have now discovered that such problems can be overcome by the incorporation in aqueous magnetic coatingcompositions of certain acrylic emulsions as hereinafter defined.

DETAILED DESCRIPTION OF THE INVENTION The magnetic coating compositions of this invention may have the following general composition:

Composition: Parts by weight Aqueous acrylic resin emulsion (45-60% solids) 40-80 Ferromagnetic pigment 30-60 Dispersing agent 0-4 Anti-foaming agent 0-5 Anti-blocking agent 0-20 Surface hardening agent 0-20 Modifying agents 0-10 In addition, any of the conventional modifiers for calendering, printing and other operations may be added to further enhance the final properties of the above magnetic coating formulation.

The acrylic resins employed in the aqueous emulsions of the present invention are methylmethacrylate-containing copolymers or terpolymers. As examples of such resins, there may be mentioned copolymers of methylmethacrylate and ethylacrylate containing at least 50% by weight of methylmethacrylate, terpolymers of butylacrylate, methylmethacrylate, and ethylacrylate containing at least 20% by Weight of butylacrylate, terpolymers of butylmethacrylate, methylmethacrylate and ethylacrylate containing at least 40% by weight of butylmethacrylate and terpolymers of methylmethacrylate, ethylacrylate and methacrylic acid containing at least 5% of methacrylic acid and the like.

Combinations of the above emulsions may of course be employed depending upon the coating technique to be employed and/or the product application. For example, a cross-linkable acrylic emulsion such as Rhoplex AC-ZOO may be employed alone or in combination with a noncross linkable acrylic resin such as AC-35 in order to achieve a particular desired film property.

The other ingredients of the combinations of the present invention listed above are all conventional agents well known in this art which, per se, form no part of this 3 4 invention. For example, the ferromagnetic oxide or oxides resistant, moisture insensitive, and possesses good adhecan be any of several which possess the necessary formusion to paper. lation and magnetic properties. Likewise, any dispersing The formulations of this invention can also be coated agent can be employed which will disperse the magnetic on film substrates and then transferred by heat and presoxide efficiently. Any of the conventional modified ma- 5 sure to other substrates without the need of a primer adheterial such as waxes, surface hardeners, anti-blocking sive. This technique exposes the high gloss finish of the agents, glossing agents, curing agents, and bodying matecoating which was previously in contact with the film to rials can be employed to further enhance a coating formuwhich it was originally applied. Transfers of this type can lation for a specific application. be accomplished by hot stamping techniques, continuous The following is a partial list of some representative laminating and similar processes. Uses in which this techagents which may be employed in the compositions of nique may be employed include the provision of magnetic the present invention: data fields on ledger cards, credit cards or any other magnetic data carrying documents. Hot stamping formula- P f; agents: tions must be somewhat frangible, self-releasing from the Ternary acetylemc glycol (SmfYnPI TG) carrier substrate, and thermoplastic at elevated tempera- Alkyl aryl polyether alcohol (Triton X-100) Potasslum tnpolyphosphate The formulations of this invention also are particular- Aerosol C-61 ly advantageous for use as coating compositions to be Anti-foaming agents:

used in the preparation of data processing tape. Such coat- SiliCOIle Oil ings must provide a dry film which is very abrasion re- NOPCO NXZ sistant, tough, smooth and of high cohesive strength. Nopco J MY The advantages provided by the compositions of the Nopco N present invention are many. Simple mixing and applica- Magnetlc oxldes: tion techniques can be used. No curing of the coating is 'Y- Sa s required. The magnetic coatings obtained possess excel- E?) 4 lent flexibility. That is, no delamination occurs when the substrate undergoes flexing during usage. The magnetic coatings obtained possess high gloss and a surface finish which is extremely smooth. Excellent adhesion to a large variety of substrates may be obtained. Little or no penetrtaion into the coating substrate occurs. In addition, the wear resistance of the coatings produced in accordance -Fe O /Fe O mixtures 'y-Fe O doped wtih cobalt or nickel Anti-blocking agent:

Amberlac 165 Surface hardening agent:

Rhoplex B-85 with the present lnvention is excellent. other modlfymg agfifnts (and The following examples will further illustrate the pres- Phenyl mel'cunc aqetate (plfiservatlve) ent invention. Examples 1-3 illustrate typical composiz l ngfgg (lonomenc acryhc resm used for tions of the present invention suitable for the techniques c oss 1 1 described above. Example 4 is a comparative example illustrating the improved results of the compositions of the present invention as compared with those of the prior phcatlons For example they can be apphed as a wet 40 art. All proportions are by weight unless otherwise indistripe by deep etch gravure or other film stripe applicaat d 11 tion techniques. When used in this manner, the composig aqueous acrylic resm emulslons have tions of the present invention provide several advantages. EXAMPLE 1 Drying of the water-based system is greatly simplified and the surface can be easily mechanically worked to a high 45 A typical specific formulation for wet striping is as gloss and excellent smoothness. There is little or no penefollows:

The above formulations are amenable to various ap- Composition Example and supplier Parts Percent Acrylic emulsion (a 40:60 ethyl acrylate and methyl methacrylate c0po1ymer).. Rhoplex AC-35 (Rohm & Haas) 73. 0 56. 4 Magnetic Pigment FezO3) ercules HR-283 60.0 38. 6

Anti blocking agent (aqueous solution of NI-I4 salt of a phthalic anhydride/cast oil alkyd Amberlac 165 (Rohm & Haas) 4. 0 3 1 s grir eggigngnrgoaagent (terpolymer of butylmethacrylate, methylmethacrylate and ethyl Rhoplex B- 1.0 8

y 1i ffiiflilfiii fgtllt lhifitiiifyh tla ffif iftfiizffif fiiifitmsinisterstamens:$ih tfifit die ifii tilif 335 3 Total 129.5 10071 tration of the binder or oxide into the substrate and flex- Similar compositions could be employed for all apibility and adhesion to the substrate are excellent. Further, the dried magnetic coating is totally insensitive to 60 phcatlons by Varying the composltlon dependmg on the product application.

moisture. Coatings of this type also offer sharp edges, good EXAMPLE 2 magnetic signals, and a very good signal-to-noise ratio.

In addition, the coating is not affected by ultraviolet ra- A specific formulation for heat transfer from a subdiation or normal environmental extremes. Wet striping strate without the use of a primer adhesive (hot stampformulations must yield a film that is tough, flexible, wearing and laminating) is as follows:

Composition Example and supplier Parts Percent Agrylicseon bilgign (terpolymer of butylacrylate, methyl methacrylate and ethyl acry- Rhoplex B-60A (Rohm & Haas) 50. 0 39. 2

Acrylic emulsion Rhoplex AC-35 (Rohm dz Haas)-.. 30. 0 23. 5

Magnetic pigment (Fe:O4) IRN (Chas. Pfizer & C0.) 40. 0 31. 3

Anti-blocking agent Amberlac (Robin & Haas) 5. 0 3. 9

Dispel-sing agent (sodium salt of polymerized alkyl aryl sulfonic aeid) Daivan No. 2 R11. Vanderbilt C0.) 0. 7 5

Antiioamlng agent N opco NXZ (Nopco Chemical Company). 2. 0 6

Total- 127. 7 100. 0

EXAMPLE 3 i and the remainder of the composition including A specific formulation for a magnetic tape coating is a magnetic pigment, and as follows: a dispersing agent capable of dispersing the mag- Composition Example and supplier Parts Percent Acrylic emulsion Rhoplex AC-35 (Rohm & Haas) 55. 48.8 Acryliic esmialsi on (terpolymer of methyl methaclylate, ethyl acrylate and methacrylic Rhoplex AO-ZOO (Rohm & Haas) 5.0 4. 4

aci :-0

Magnetic pigment (F9304) MO-2035 (Chas. Pfizer dz Co.) 48.0 42. 6 Dispersing agent Aerosol C-61 (American Cyanamid) 1. 0 .9 Antiforming agent Nopco NXZ (Nopco Chemical Company) 0.8 7 Conductive carbon Conductex SC (Columbian Carbon 00.) 3.0 2.6

Total 112. 8 100. 0

EXAMPLE 4 netic pigment.

2. An aqueous magnetic coating composition comprising, by Weight, approximately 53% of an aqueous acrylic resin emulsion having 45-60% solids consisting of In order to compare the properties of coatings produced by the present invention with those of the prior art, the following compositions were prepared.

(A) Prior art coating compositio a methylmethacrylate-ethyl acrylate copolymer Composition: Parts by wt containing over 50% by weight of methylmeth- Styrene-butadiene copolymer latex (60:40) 117.0 acrylate, and F6203 (HR 233) 1672 a rpolym r f methylmethacrylate, ethyl acrylate Sodium aiginate 33 and me hacrylic acid containing approx mately sodium pglyphgsphate 50% y c y t and appr ximately Polyethylene glycol laurate 1.0 methacryhc water 2500 he ratlo f opolymer to terpolymer being of the order of about 10:1, and the remainder of the corn- (B) Compos1t1on of this invention Position including Composition: Parts by Wt. 39 a magnetic pigment,

Acrylic latex (AC-) 54.75 pprox m cly 1% dispersing agent capable of Fe O (HR-283) 37.5 i p rsing the ferromagnetic oxide pigment, and Amberlac 165 3.0 approximately 1% antifoaming agent, Acryloid B-85 0.75 3. The coating composition of claim 2 wherein the Aerosol C-61 0.75 35 magnetic pigment comprises over 40% by weight of Nopco NXZ 0.4 Fe O 4. An aqueous magnetic coating composition consist- Two additional coatings, C and D, were also formug essentially of lated as in A, substituting, respectively, Rhoplex B-lS and Rhoplex disclosed by colwin et and 55 parts by weight of an aqueous acrylic resin emulsion Levine, supra, for the styrene-butadiene copolymer latex. 40 havmg 60% sends and constltutlng a C POIYmcI' The above compositions were each then coated on white flmethylmcthacryl ate and hyl acrylate (substancardstock and 1 mil Mylar film and air dried. The retla 1y g Y sultant samples were then subjected to testing to deter- 5 Rafts Y of f ajllueolils yll rcsln emulsmine their resistance to moisture and elevated tempera- 5111 havlng 5011(15 collstltlltlng a p y ftures. The results of these tests are set forth below. 45 of methyl?thacryliilte,v hyl acrylate and methacrylic Coating A B C D l3 llent Exccllent. Excellent. Ad e o to cardstock to yla geugoomfl WW gem (2) Abrasion resistance (5 stroke-Sutherland) Poor Good. 00

A v A Excellcut Excellent for up to 5 manual folds. (3) Mexlblhtyxk Good 0 r n t EPoplr aiter l0 fold 4 Wet rub stren th* (3 scc.in11ne1si0n) Very poor d0 ixce en ice on E5; Blocking (at 1 60 F. against cardstock) N None. V2230 Slight tackmess.

6 Blockin at 160 F. ink to ink) Sevele Severe E7; Resistafic to thermal deiormation* Fair- Good..- Poor Poor.

*As applied to both cardstock and polyester (Mylar) film.

acid (substantially :30:20 by weight),

What is claimed is: 48 parts by weight of magnetic pigment, 1. An aqueous magnetic coating composition compris- 6O 1 P Y Welghi Of a dlspefslllg agent capable of sing by Weight persing the ferromagnetic oxide pigment,

1 part antifoaming agent, and

f n eous acr lic resin bet ween about 53 and 63% o a aqu y 3 parts ctive carbon.

emulsion having 45-60% solids, consisting of a methylmethacrylate-ethyl acrylate copolymer contam- References Cited ing by Weight of methylmethacrylate, and 65 a terpolymer of methylmethacrylate and ethyl acrylate UNITED STATES PATENTS and a third compound taken from the class consisting 3,023,123 2/1962 Colwill et a1 1l744 of butyl acrylate, butylmethacrylate and methacrylic 3,240,621 3/1966 wer ct a1. 117-932. acid, the butylmethacrylate being employed in 08% 3,200,007 8/1965 Flowers 117-'1'38.8

of terpolymer for wet striping applications, the butylacrylate being employed in 39.2% of terpolymer for PATRICK GARVIN Primary Exammer heat-transferred coatings, and the methacrylic acid Assistant Examiner being employed in 4.4% of terpolymer for magnetic. US. Cl. X.R. tape coating applications, 117-44, 235 

